Exodon Paradoxus without a doubt.
If you want to see some true shoaling characteristics, watch a tank full of these guys. Non stop action. This species never gets boring.
personaly I like corys,they aren't that good looking,but they are really fun to watch and I agree with truck,Trigonostigma Hengeli are lovely little fish
My favorites are Discus, Praecox Rainbows, Cardinal Tetras, and Cherry Barbs. Also if you are looking to get more schooling fishes can you please specify the tank size and water conditions so i can tell you my personal favorites for your parameters.
i would say cory's,Guppy's,mollies,tetras,harliquins i just go some of those,and i plan to get the elusive endlerguppys that i never see in my area on this lovely plant